Timer/TimerTask Error

Question

I just started with programming of android applications and right now I have a problem with timer and timer tasks.

In my app I use a timer to update the UI but when I start to test it gets an error and I have to force close it.

Here is my timer code:

int delay = 5000; // delay for 5 sec.
int period = 1000; // repeat every sec.

Timer timer = new Timer();
timer.scheduleAtFixedRate(new TimerTask() 
{
    public void run() 
    {
        moveLettersInCircle();

    }

}, delay, period);

Logcat says this:

07-30 18:40:12.635: D/dalvikvm(334): GC_EXTERNAL_ALLOC freed 61K, 52% free 2599K/5379K, external 1625K/2137K, paused 52ms
07-30 18:40:16.186: D/dalvikvm(334): GC_EXTERNAL_ALLOC freed 36K, 51% free 2672K/5379K, external 3792K/4025K, paused 40ms
07-30 18:40:21.503: W/dalvikvm(334): threadid=9: thread exiting with uncaught exception (group=0x40015560)
07-30 18:40:21.526: E/AndroidRuntime(334): FATAL EXCEPTION: Timer-0
07-30 18:40:21.526: E/AndroidRuntime(334): android.view.ViewRoot$CalledFromWrongThreadException: Only the original thread that created a view hierarchy can touch its views.
07-30 18:40:21.526: E/AndroidRuntime(334):  at android.view.ViewRoot.checkThread(ViewRoot.java:2932)
07-30 18:40:21.526: E/AndroidRuntime(334):  at android.view.View.requestLayout(View.java:8267)
07-30 18:40:21.526: E/AndroidRuntime(334):  at android.view.View.requestLayout(View.java:8267)
07-30 18:40:21.526: E/AndroidRuntime(334):  at android.view.View.requestLayout(View.java:8267)
07-30 18:40:21.526: E/AndroidRuntime(334):  at android.view.View.requestLayout(View.java:8267)
07-30 18:40:21.526: E/AndroidRuntime(334):  at android.widget.RelativeLayout.requestLayout(RelativeLayout.java:257)
07-30 18:40:21.526: E/AndroidRuntime(334):  at android.view.View.requestLayout(View.java:8267)
07-30 18:40:21.526: E/AndroidRuntime(334):  at android.widget.RelativeLayout.requestLayout(RelativeLayout.java:257)
07-30 18:40:21.526: E/AndroidRuntime(334):  at android.view.View.requestLayout(View.java:8267)
07-30 18:40:21.526: E/AndroidRuntime(334):  at android.view.View.setLayoutParams(View.java:5000)
07-30 18:40:21.526: E/AndroidRuntime(334):  at com.jest.womix.Game$1.run(Game.java:104)
07-30 18:40:21.526: E/AndroidRuntime(334):  at java.util.Timer$TimerImpl.run(Timer.java:284)
07-30 18:40:25.666: I/Process(334): Sending signal. PID: 334 SIG: 9

How can I solve this ?

Edited HANDLER Code:

    Handler m_handler;
    Runnable m_handlerTask;  
    m_handler = new Handler();   
    m_handlerTask = new Runnable()
    {
      @Override 
      public void run() { 

        moveLettersInCircle(); 
        m_handler.postDelayed(m_handlerTask, 1000);  //Problem: The local variable m_handlerTask may not have been initialized --> But if I initialize it then I get another error in the line m_handlerTask = new Runnable()

      }
      };
     m_handlerTask.run();  

Best regards

Answer 1

I guess you are updating ui from the backgroudn thread. Timer runs on a different thread.

You should update ui on the ui thread. Use runOnUiThread

  runOnUiThread(new Runnable() {

                    @Override
                    public void run() {
                       // update ui here.
                    }
                });

android.view.ViewRoot$CalledFromWrongThreadException: Only the original thread that created a view hierarchy can touch its views.

The above generally means you are updaint/acessing ui from another thread.

You can also use a Handler

Handler m_handler;
Runnable m_handlerTask ;  
m_handler = new Handler();   
m_handlerTask = new Runnable()
{
  @Override 
  public void run() { 

    // do something  
    m_handler.postDelayed(m_handlerTask, 1000);    

  }
  };
 m_handlerTask.run();   

To cancel the run m_handler.removeCallbacks(m_handlerTask).

Edit:

     timer.scheduleAtFixedRate( new TimerTask() {
            @Override
            public void run() {

               runOnUiThread(new Runnable() //run on ui thread
                 {
                  public void run() 
                  { 
                    // update ui here
                  }
                  });
            }
        }, 1000, 1000 );